Compressors in rail vehicles are subject to a variety of, in part, conflicting demands, such as for example a high delivery output, adequate activation duration, low sound emissions, low energy consumption, a small structural space, and low purchase and life-cycle costs. Here, the compressor may satisfy extremely different demand profiles depending on the operating state of the rail vehicle. The typical problem in designing a compressor is that of finding the best comprise between these demands which is acceptable in all operating states of the rail vehicle. In general, electrically driven compressors are used in rail vehicles. The operation of the compressors takes the form of on/off operation with a constant rotational speed, the so-called rated rotational speed, between the lower activation and the upper deactivation pressure. The compressor is dimensioned such that a predefined filling time is attained and a minimum activation duration during operation is not undershot.
From the generally known prior art, it emerges that, between the different operating states of the rail vehicle, there is no difference in the operation of the compressor. Here, the fan of the cooling system is subject to the same operating regime as the compressor, as the fan is generally directly jointly driven by the compressor.
During a filling phase, the compressor is operated at the rated rotational speed. The rated rotational speed is selected such that the compressor can be operated continuously. Furthermore, the structural size of the compressor is selected such that, during track operation, a minimum activation duration is not undershot, and the maximum filling time is not overshot. During track operation, the compressor is operated intermittently. In this case, the compressor is started when the pressure in the compressed-air vessel has fallen to the activation pressure. When the deactivation pressure is reached in the compressed-air vessel, the compressor is operated at the rated rotational speed. The compressor is deactivated when the deactivation pressure is reached, and is restarted only when the pressure has dropped to the activation pressure. In the case of electrically driven rail vehicles, the drive motor is used as an electrodynamic brake during a braking phase. In the process, electrical energy is generated, wherein it is often not economical, or is in part impossible, for the electrical energy to be fed back into the electrical grid. During station operation, when the rail vehicle is stopped at a station, the compressor is operated intermittently, as it is during travel. Since there is no dominant travelling noise, sound emissions of the compressor and of the fan may be avoided. Since, when at a station, the pneumatic suspension exhibits an increased air demand owing to the embarking/disembarking of passengers, this often leads to the activation of the compressor and of the fan, and thus to undesired sound emissions while the rail vehicle is stopped at the station. Furthermore, in particular in the case of regional transport, rail vehicles are often parked in the vicinity of residential areas in an energized state, for example to prevent freezing. Here, sound emissions may be prevented to the greatest possible extent. Owing to leakage, it is often the case that the pressure in the compressed-air vessels falls to the lower activation pressure of the compressor overnight, such that refilling is necessary, and the compressor is operated intermittently at rated rotational speed. In this case, not only the sound emissions of the compressor but also further noises, such as for example the disturbing ventilation noise of the air dryer, are generated.